What is a bone scan?

What is the difference between a bone scan and a bone density scan?

• Answer:

  Bone scans are performed by injecting a radioactive material, that is taken up more rapidly by bone with a relatively high metabolic rate than by bone with a relatively low metabolic rate. In other words, in regions of bone where the bone tissue is undergoing rapid change, the radioactive material will concentrate to a greater degree. Examples of areas where this rapid change occurs are fractures, tumors, areas of inflammation (arthritis), etc. The radioactivity is then read by a special detector which produces an image of the skeleton, enhanced by areas of increased metabolic activity. Bone density scans, on the other hand, are performed with specialized x-ray equipment. It has been known for a long time that a bone's strength is related to how much calcium and other minerals are contained in the bone tissue. It has been further known that bone mineral tends to absorb x-rays. This is why x-rays show bones so well. The bone density (or DEXA) scan measures how much the x-rays are absorbed by the bones and then calculates the relative density of that bone. By comparing the number generated with the normal values, it can be determined whether a patient's bones are abnormal. This test is used primarily to diagnose osteoporosis.